As a conventional vehicle straight-line performance adjustment method of this type, a method including determining a drift of a vehicle based on whether an input of a load cell that measures the side force is equal to or lower than a specified value or equal to or larger than the specified value, allowing an operator to adjust a balance so as to reduce the drift amount, and measuring the side force again is disclosed in, for example, Japanese Patent Application Laid-Open No. H6-331505.
With such a conventional method, however, adjustment and measurement are performed several times repeatedly, so that an accurate adjustment value cannot be indicated to the operator. The adjustment operation, therefore, relies on the operator, with the result that an accurate drift amount cannot be acquired.
A technique for making an alignment adjustment so as to minimize a force in a roller rotation axis direction, measuring a stability with high accuracy, and enabling easily adjusting the straight-line performance of the vehicle without the need for each manufacturer to refer to a target alignment value set for each vehicle type is disclosed in, for example, Japanese Patent Application Laid-Open No. H7-5076.
This conventional technique has, however, the following disadvantages. It is necessary to adjust all wheels so as to perform the alignment adjustment. It takes lots of time for an adjustment operation. Each manufacturer fails to refer to the target value set for each vehicle type.
A technique for detecting a moving amount of each abutment body that abuts on a side surface of a vehicle, and making a toe adjustment so that the moving amount is equal to or smaller than a certain value, wherein a vehicle toe adjustment is performed while a position of the abutment member is adjusted so that an abutment pressure of the abutment body is equal to each other on right and left side of the vehicle, is disclosed in, for example, Japanese Patent Application Laid-open No. H9-210863.
This technique has, however, the following disadvantages. The toe adjustment can be made in a free state equal to an actually moving state of the vehicle by abutting right and left abutment bodies on the vehicle with a constant force while moving the right and left abutment bodies. Similarly to the technique described in the Japanese Patent Application Laid-Open No. H6-331505, therefore, an accurate adjustment value cannot be indicated to an operator. As a result, an adjustment operation relies on the operator, and an accurate drift amount cannot be acquired.
A technical theme of the present invention has been achieved in light of the conventional disadvantages. It is an object of the present invention to provide a vehicle straight-line performance adjusting method capable of performing an adjustment operation for a vehicle straight-line performance surely in a short time without the need of operator's skill.